1. Field of the Invention
The present invention relates, in general, to fluid compressing apparatus. In particular, the invention relates to a fluid compressing apparatus used for a refrigerating apparatus. The fluid compressing apparatus is provided with a lubricating fluid material used for rotatable contacting portions of the fluid compressing mechanism thereof. The lubricating fluid material is stored in the fluid compressing apparatus together with refrigerant.
2. Description of the Related Art
Various types of a fluid compressing apparatus are used for a refrigerating cycle in a household refrigerating system. One common type may be a rotary type fluid compressor. The rotary type fluid compressor typically includes a compressing section and a driving section, i.e., motor, which drives the compressing section arranged in a sealed housing. The middle portion of a rotational shaft extending from the driving section is rotatably supported by a fixed frame mounted on the inner wall of the sealed housing. The extended end portion of the rotational shaft projecting through the fixed frame is connected to the roller of the compressing section, and the roller is rotated in the compressing chamber formed in the fixed frame.
In such a rotary compressor used for a refrigerating apparatus, the CFC-12 refrigerant (CCL.sub.2 F.sub.2) is used as a fluid to be compressed. The CFC-12 Refrigerant (polyhalide hydrocarbon) is a kind of flon (chlorofluorocarbon). In general, flon is easily liquidized by applying pressure, and has nonflamable and innoxious properties. Thus, such a flon has been widely used as refrigerant, atomizing agent, extinguishing agent. etc. However, specific kinds of flon including chlorine (Cl) rarely decompose in the air because of their chemical stability and have been said to destroy the earth's ozone layer. At the present time, use of such specific kinds Of flon are intended to be globally controlled to avoid destruction of the ozone layer. Thus, the HFC-134a refrigerant (CH.sub.2 FCF.sub.3 ) is proposed as a substitute for such specific kinds of flon, e.g., CFC-12 refrigerant. Since the HCF-134a refrigerant has no chlorine (Cl) in its chemical composition, it does not harm the ozone layer.
In view of the mutual solubility of the HCF-134a refrigerant and lubricating oil, use of a synthetic lubricating oil of polyglycol e.g., polyalkyleneglycol, (hereinafter referred to as PG) has been considered when the above-described HFC-134a refrigerant is used as a fluid to be compressed. However, the viscosity-pressure coefficient (.alpha.) of the PG is less than approximately 50% of that of a generally known mineral oil, e.g., a naphthene system mineral oil. Thus, since the oil film thickness formed by the PG is extremely thin, as compared with that of a naphtene system mineral oil, there is a possibility of a burn-in caused by the rotational contact of metal surfaces of the rotational shaft and its bearing portion if the PG is used in the conventional fluid compressor.
To avoid the above-described problem, it has been suggested that the viscosity of the PG be increased to increase the oil film thickness of the PG between the rotational shaft and its bearing portion. However, an increase in the viscosity of the PG results in an increase in the slide-resistance between the rotational shaft and its bearing portion. In particular, the viscosity of the PG is increased as the external temperature decreases, resulting in an increase in the power consumption.